Kennedy, the son of former U.S. Rep. Joseph Kennedy II and a grandson of the late Robert F. Kennedy, is running for the Congressional seat which will be vacated by Democratic Rep. Barney Frank when he retires at the end of his term.

In the first quarter of 2012, Kennedy raised $1.3 million with about half of the donations coming from donors giving $100 or less, according to an email to supporters. Among Republican competition, Kennedy's chief rival, Sean Bielat, raised $175,000 in the same period, with an average donation of $90 according to Bielat's campaign.

Former state mental health commissioner Elizabeth Childs is also seeking the Republican nomination.

Kennedy, who was endorsed last week by the Massachusetts Nurses Association, said he appreciates the nod of support.

“I am honored to have the support of the Professional Fire Fighters of Massachusetts,” Kennedy said in a statement. “These brave men and women are an example of the very best in public service. They work around the clock to keep our families and communities safe, oftentimes putting their own lives at risk to protect those of neighbors, friends, and strangers. They understand exactly what is at stake in this election, and their support for my campaign will be invaluable.”

Established in 1945, the Professional Fire Fighters of Massachusetts includes nearly 200 IAFF Local unions representing more than 12,000 fire fighters across Massachusetts.